Thirteen soldiers and four military crewmembers were killed in the crash in a mountainous part of Pervari district in Siirt province, in southeastern Turkey, where the rebel Kurdistan Worker's Party is fighting for self-rule.

President Abdullah Gul said the soldiers were on their way "to help their friends" in an operation against the rebels who have escalated attacks in recent months, adding the incident would not deter Turkey from its determination to fight the rebels.

The provincial governor, Ahmet Aydin, blamed the crash on heavy fog and ruled out an attack by the rebel group.

"The weather during the transportation (of troops) was bad. There was extreme rain. The helicopter crashed into rocks because of the fog," Aydin said in televised statements. "The incident was the result of a crash and any kind of an attack is out of the question."

The Kurdish rebels have been fighting since the 1980s and they seek more rights for Kurds, including autonomy in the mostly Kurdish southeast of the country. Turkey and its Western allies categorize the rebels, known by the acronym PKK, as a terrorist group.

On Friday, the office for the governor for the nearby province of Hakkari said as many as 42 Kurdish rebels had been killed in the past three days in operations that were backed by airpower. It made no mention of any casualties among troops.

Several days ago, Turkish media reported that Turkish soldiers were airlifted into northern Iraq for a brief operation against suspected rebels, who have bases there. There were no reports of casualties on that mission. Turkey periodically carries out artillery and air strikes on PKK positions in northern Iraq, but reports of cross-border incursions by troops are rare.